Field of the Invention
The present invention relates generally to tight shut-off valves such as plug valves or ball valves and more specifically, to such valves which also have a flow control element mounted in the waterway of the plug valve or the ball valve to provide a flow control capability for modulating flow in the opened position of the valve.
Prior Art
Typically, conventional plug valves or ball valves provide a tight shut-off capability designed either to prevent total flow through the valve in one configuration or provide for 100% of flow through the valve in the other configuration. By way of example, one such valve is disclosed in U.S. Pat. No. 3,011,513 which describes a twin seal plug valve capable of double block and bleed performance. Such a prior art valve is designed to completely shut-off the flow of fluid through the valve when the passageway through the plug is oriented at 90 degrees with respect to the connecting inlet and outlet pipes. Furthermore, such prior art valves are designed to permit 100% flow through the valve when the plug passage is oriented coaxially with the inlet and outlet pipes. Such valves are not designed to provide a means for controlling the flow rate of the fluid through the valve in the open position whereby the flow of fluid through the valve is in the range between the closed and fully opened position such as where the fluid flow rate would be for example only 50% of the maximum flow rate capability of the valve.
There is prior art which discloses means for controlling the flow rate of a plug-type or ball-type valve so that the maximum flow rate can be limited to be less than the capability of the valve in its fully opened position. However, there does not appear to be any prior art which permits such control in a continuously variable configuration which allows simple and expedient changes in the flow rate through the valve element using the operator that would normally be used to control the open and close position of the valve. By way of example, U.S. Pat. No. 2,140,292 to Jensen discloses means for providing a fixed maximum flow regulating orifice that is concentric with the main shut-off plug. However, Jensen does not provide for continuous modulation of the secondary control element by the common valve operator after the main shut-off plug has reached the full open position. Similarly, U.S. Pat. No. 3,526,249 to Baustian discloses a control valve which has an adjustable "preset" maximum opening but again does not disclose a continuously variable secondary element within the main blocking plug directly operable by means of the same main operator that controls the opened and closed position of the plug itself. Thus, although the prior art provides various valve designs which permit a form of flow control in a plug or ball-type valve, the relatively fixed configuration of each such flow control scheme still leaves a substantial need for a valve design which permits convenient and readily accessible flow control variation in such a valve using the same operator that the user would otherwise employ to open and close the valve in its conventional configuration.